1. Field of the Invention
This invention relates generally to body invasive catheter arrangements including conductive lead assemblies for coupling an electrical device, such as a cardiac pacemaker, to an organ to be stimulated or monitored by conducting signals bi-directionally between the two, to ventriculography catheters for performing various diagnostic procedures, and more particularly to unique catheter constructions which combine multiple electrodes and/or lumens in a small diameter shaft, while maintaining the properties of flexibility, torque control, biocompatibility, resistance to entry of body fluids, and high reliability over prolonged periods of time.
2. Discussion of the Prior Art
Early cardiac pacer systems, by today's standards, were quite primative in that they generally involved a simple asynchronous pulse generator which produced pulses at a fixed rate, the pulses being applied to the heart muscle by way of a single-conductor, unipolar lead and an electrode generaly disposed at the distal tip thereof. Later, bipolar leads were employed in which two electrode surfaces were disposed at the distal end of the lead assembly and the electrical stimulation pulses were applied across these two surfaces. Later yet, so-called demand pacers were introduced in which the electrodes are used for both stimulating the heart muscle and for sensing the natural electrical activity of the heart.
More recently, cardiac pacer systems have become significantly more sophisticated. Pacemaker electronics have improved to the extent that isolated conductive pathways are needed to utilize the accuracy of the sensing circuitry. The energy transmitted via the catheter or lead assembly to artificially pace the heart require, the use of sense circuits in the pacemaker that either momentarily shut off or are blinded during the pacing pulse episode, whereby intermittent sensing of intrinsic heart activity results. There is a need, however, for separate, dedicated conduction pathways so that continuous sensing of cardiac activity can take place.
With the advent of digital, programmable pacemakers constructed using integrated circuit techniques, an increasing number of functions can be performed by the circuits in the implantable pacer. For example, selective pacing and/or sensing in the plural chambers of the heart can be realized. A two-way communication between the implanted pacer and an external programmer/diagnostic device is required in order to take advantage of the capabilities of current pacer designs. Before the conditions being sensed by the implanted pacer can be communicated to the external device, the implanted device must be able to sense and store various physiologic parameters, such as, P-wave and R-wave artifacts, capture verification signals, impedance changes resulting from the beating action of the heart, etc.
As pacer devices become more sophisticated, the lead sets used therewith have also increased in complexity, creating an increasing need to develop multiple sensor mechanisms within a single lead shaft to better represent and respond to physiologic need. With each sensor system, a set of electrically insulated conductors are necessary to insure sensor isolation. In that these leads are often threaded through the body's vascular system, it is imperative that the overall diameter of the lead be minimized. Also, because lives may be at stake, it is essential that the leads perform reliably over prolonged periods in a somewhat hostile environment.
It is also necessary to properly balance the physical properties of the leads to minimize the likelihood of dislodgement from the site of fixation to the organ and to minimize irritation to surrounding tissue such that stimulation thresholds are minimized and remain substantially constant. Thus, it is a desirable property of a pacer lead assembly that it be highly flexible without preferance to any rotational axis while providing a desired degree of torque transmission which, of course, facilitates the routing of the leads through the vascular system during the implantation operation.
Besides implantable pacemaker lead catheters, there are various other types of catheters useful in the diagnosis of organ abnormalities and in the treatment thereof. Angiographic procedures are commonly employed to detect occluded vessels, malfunctioning heart valves and myocardiopathy. These procedures involve the temporary insertion of a tubular catheter having at least one open lumen and the injection of a radio-opaque dye through that lumen while the patient is being examined with a fluoroscope. More sophisticated ventriculographic catheters may include electrodes for pacing and/or measuring electrical field phenomena and/or transducers for monitoring pressure and/or thermistors for measuring temperatures when thermodilution techniques are being employed to measure the stroke volume or other hemodynamic characteristics of the heart.
It may also be desirable, on occasion, to have a cardiac catheter which embodies plural lumens within a single shaft, along with electrical sensing capabilities of the type described above. For example, ports may be positioned along the length of the tubular shaft toward the distal end thereof which communicate with separate lumens extending longitudinally through the shaft so that pressures may be monitored at predetermined points by suitable pressure sensing equipment connected at the proximal end of the catheter. Also, a balloon-type structure may be affixed to the outer wall of the shaft near its distal end, the ballon being inflatable at the proximal end of the catheter shaft by the injection of a suitable fluid through a lumen having a port communicating with the zone covered by the balloon. Such balloons are commonly found on so-called flow-directed catheters in which the balloon helps float the distal end of the catheter through the heart and is used as an anchoring means for holding the catheter in a desired position within the vascular system.
Current technologies involved in both cardiac pacing systems and temporary cardiac monitoring systems have merged, resulting in both short and long term implant configurations of greater complexity and sophistication, with the corresponding overall increase in diameter. This increase in capabilities and sophistication translate to: (1) More electrodes in a greater variety of shapes and/or locations with a corresponding increase in the number of conductors. (2) The incorporation of fluid carrying conduits or lumens and their associated portings; while maintaining the overall diameter, handling characteristics, reliability, and bio-compatability so essential to these applications. A need has therefore arisen for an implantable lead construction that increases the number of conductors and/or fluid channels and/or electrodes without significantly increasing the overall diameter of the catheter or degrading the handling characteristics of the device, i.e., torque control, flexiblity, etc.